The following discussion is provided solely to assist the understanding of the reader, and does not constitute an admission that any of the information discussed or references cited constitute prior art to the present invention.
Many important infectious diseases afflicting mankind are caused by viruses. Many of these diseases, including rabies, smallpox, poliomyelitis, hepatitis, yellow fever, immune deficiencies and various encephalitic diseases, are frequently fatal. Others are significant in that they are highly contagious and create acute discomfort such as influenza, measles, mumps and chickenpox, as well as respiratory or gastrointestinal disorders. Others such as rubella and cytomegalovirus can cause congenital abnormalities. Finally there are viruses, known as oncoviruses, which can cause cancer in humans and animals.
Among viruses, the family of Herpesviridae is of great interest. The Herpesviridae are a ubiquitous class of icoshedral, double stranded DNA viruses. Of over 100 characterized members of Herpesviridae (HHV), only eight infect humans. The best known among these are Herpes simplex type 1 (HSV-1), Herpes simplex type 2 (HSV-2), Varicella zoster (chicken pox or shingles), cytomegalovirus (CMV) and Epstein-Barr virus (EBV). The prevalence of Herpes viruses in humans is high, affecting at least one third of the worldwide population; and in the United States, 70-80% of the population have some kind of Herpes infection. While the pathology of Herpes infections are usually not dangerous, as in the case of HSV-1 which usually only causes short lived lesions around the mouth and face, these viruses are also known to be the cause of more dangerous symptoms, which vary from genital ulcers and discharge to fetal infections which can lead to encephalitis (15% mortality) or disseminated infection (40% mortality).
Herpes viruses are highly disseminated in nature and highly pathogenic for man. For example, Epstein-Barr virus (EBV) is known to cause infectious mononucleosis in late childhood or adolescence or in young adults. The hallmarks of acute infectious mononucleosis are sore throat, fever, headache, lymphadenopathy, enlarged tonsils and atypical, dividing lymphocytes in the peripheral blood. Other manifestations frequently include mild hepatitis, splenomegaly and encephalitis. EBV is also associated with two forms of cancer: Burkitt's lymphoma (BL) and the nasopharyngeal carcinoma (NPC). In endemic areas of equatorial Africa, BL is the most common childhood malignancy, accounting for approximately 80% of cancers in children. While moderately observed in North American Caucasians, NPC is one of the most common cancers in Southern China with age incidence of 25 to 55 years. EBV, like the cytomegalovirus, is also associated with post-transplant lymphoproliferative disease, which is a potentially fatal complication of chronic immunosuppression following solid organ or bone marrow transplantation.
Other diseases are also associated with HSV, including skin and eye infections, for example, chorioretinitis or keratoconjunctivitis. Approximately 300,000 cases of HSV infections of the eye are diagnosed yearly in the United States.
AIDS (acquired immunodeficiency syndrome) is caused by the human immunodeficiency virus (HIV). By killing or damaging cells of the body's immune system, HIV progressively destroys the body's ability to fight infections and certain cancers. There are currently approximately 42 million people living with HIV/AIDS worldwide. A total of 3.1 million people died of HIV/AIDS related causes in 2002. The ultimate goal of anti-HIV drug therapy is to prevent the virus from reproducing and damaging the immune system. Although substantial progress has been made over the past fifteen years in the fight against HIV, a cure still eludes medical science. Today, physicians have more than a dozen antiretroviral agents in three different drug classes to manage the disease. Typically, drugs from two or three classes are prescribed in a variety of combinations known as HAART (Highly Active AntiRetroviral Treatment). HAART therapies typically comprise two nucleoside reverse transcriptase inhibitors drugs with a third drug, either a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor. Clinical studies have shown that HAART is the most effective means of reducing viral loads and minimizing the likelihood of drug resistance.
While HAART has been shown to reduce the amount of HIV in the body, commonly known as viral load, tens of thousands of patients encounter significant problems with this therapy. Some side effects are serious and include abnormal fat metabolism, kidney stones, and heart disease. Other side effects such as nausea, vomiting, and insomnia are less serious, but still problematic for HIV patients that need chronic drug therapy for a lifetime.
Currently approved anti-HIV drugs work by entering an HIV infected CD4+ T cell and blocking the function of a viral enzyme, either the reverse transcriptase or a protease. HIV needs both of these enzymes in order to reproduce. However, HIV frequently mutates and become resistant, rendering reverse transcriptase or protease inhibitor drugs ineffective. Once resistance occurs, viral loads increase and dictate the need to switch the ineffective agent for another antiretroviral agent. Unfortunately, when a virus becomes resistant to one drug in a class, other drugs in that class may become less effective. This phenomenon known as cross-resistance, occurs because many anti-HIV drugs work in similar manners. The occurrence of drug cross-resistance is highly undesirable because it reduces the available number of treatment options for patients.
There is therefore a great need for the development of other antiviral agents effective against HIV that work through other mechanisms of action against which the virus has not developed resistance. This is becoming especially important in view of recent data showing that 1 out of 10 patients newly diagnosed with HIV in Europe, is infected with a strain of HIV already resistant to at least one of the approved drug on the market.
Respiratory syncytial virus (RSV) causes upper and lower respiratory tract infections. It is a negative-sense, enveloped RNA virus and is highly infectious. It commonly affects young children and is the most common cause of lower respiratory tract illness in infants. RSV infections are usually associated with moderate-to-severe cold-like symptoms. However, severe lower respiratory tract disease may occur at any age, especially in elderly or immunocompromised patients. Children with severe infections may require oxygen therapy and, in certain cases, mechanical ventilation. According to the American Medical Association, an increasing number of children are being hospitalized for bronchiolitis, often caused by RSV infection. RSV infections also account for approximately one-third of community-associated respiratory virus infections in patients in bone marrow transplant centers. In the elderly population, RSV infection has been recently recognized to be very similar in severity to influenza virus infection.
Influenza (INF), also known as the flu, is a contagious disease that is caused by the influenza virus. It attacks the respiratory tract in humans (nose, throat, and lungs). An average of about 36,000 people per year in the United States die from influenza, and 114,000 per year require hospitalization as a result of influenza.
In all infectious diseases, the efficacy of a given therapy often depends on the host immune response. This is particularly true for herpes viruses, where the ability of all herpes viruses to establish latent infections results in an extremely high incidence of reactivated infections in immunocompromised patients. In renal transplant recipients, 40% to 70% reactivate latent HSV infections, and 80% to 100% reactivate CMV infections. Such viral reactivations have also been observed with AIDS patients.
The hepatitis B virus (HBV) is a DNA virus that belongs to the Hepadnaviridae family of viruses. HBV causes hepatitis B in humans. It is estimated that 2 billion people have been infected (1 out of 3 people) in the world. About 350 million people remain chronically infected and an estimated 1 million people die each year from hepatitis B and its complications. HBV can cause lifelong infection, cirrhosis of the liver, liver cancer, liver failure, and death. The virus is transmitted through blood and bodily fluids. This can occur through direct blood-to-blood contact, unprotected sex, use of unsterile needles, and from an infected woman to her newborn during the delivery process. Most healthy adults (90%) who are infected will recover and develop protective antibodies against future hepatitis B infections. A small number (5-10%) will be unable to get rid of the virus and will develop chronic infections while 90% of infants and up to 50% of young children develop chronic infections when infected with the virus. Alpha-interferon is the most frequent type of treatment used. Significant side effects are related to this treatment including flu-like symptoms, depression, rashes, other reactions and abnormal blood counts. Another treatment option includes 3TC which also has many side effects associated with its use. In the last few years, there has been an increasing number of reports showing that patients treated with 3TC are developing resistant strains of HBV. This is especially problematic in the population of patients who are co-infected with HBV and HIV. There is clearly an urgent need to develop new antiviral therapies against this virus.
Hepatitis C virus (HCV) infection is the most common chronic bloodborne infection in the United States where the number of infected patients likely exceeds 4 million. This common viral infection is a leading cause of cirrhosis and liver cancer, and is now the leading reason for liver transplantation in the United States. Recovery from infection is uncommon, and about 85 percent of infected patients become chronic carriers of the virus and 10 to 20 percent develop cirrhosis. It is estimated that there are currently 170 million people worldwide who are chronic carriers. According to the Centers for Disease Control and Prevention, chronic hepatitis C causes between 8,000 and 10,000 deaths and leads to about 1,000 liver transplants in the United States alone each year. There is no vaccine available for hepatitis C. Prolonged therapy with interferon alpha, or the combination of interferon with Ribavirin, is effective in only about 40 percent of patients and causes significant side effects.
Today, the therapeutic outlook for viral infections in general is not favourable. In general, therapies for viruses have mediocre efficacies and are associated with strong side effects which either prevent the administration of an effective dosage or prevent long term treatment. Three clinical situations which exemplify these problems are herpesviridae, HIV and RSV infections.
In the case of herpesviridae, there are five major treatments currently approved for use in the clinic: idoxuridine, vidarabine, acyclovir, foscarnet and ganciclovir. While having limited efficacy, these treatments are also fraught with side effects. Allergic reactions have been reported in 35% of patients treated with idoxuridine, vidarabine can result in gastrointestional disturbances in 15% of patients and acyclovir, foscarnet and ganciclovir, being nucleoside analogs, affect DNA replication in host cells. In the case of ganciclovir, neutropenia and thrombocytopenia are reported in 40% of AIDS patients treated with this drug.
While there are many different drugs currently available for the treatment of HIV infections, all of these are associated with side effects potent enough to require extensive supplemental medication to give patients a reasonable quality of life. The additional problem of drug resistant strains of HIV (a problem also found in herpesviridae infections) usually requires periodic changing of the treatment cocktail and in some cases, makes the infection extremely difficult to treat.
The treatment of RSV infections in young infants is another example of the urgent need for new drug development. In this case, the usual line of treatment is to deliver Ribavirin by inhalation using a small-particle aerosol in an isolation tent. Not only is Ribavirin only mildly effective, but its uses is associated with significant side effects. In addition, the potential release of the drug has caused great concern in hospital personnel because of the known teratogenicity of Ribavirin.
It is clear that for any new emerging antiviral drug being developed, it would be highly desirable to incorporate the three following features: 1—improved efficacy; 2—reduced risks of side effects and 3—a mechanism of action which is difficult for the virus to overcome by mutation.
Several attempts to inhibit particular viruses by various antisense approaches have been made.
Zamecnik et al. have used ONs specifically targeted to the reverse transcriptase primer site and to splice donor/acceptor sites (Zamecnik, et al (1986) Proc. Natl. Acad. Sci. USA 83:4143-) (Goodchild & Zamecnik (1989) U.S. Pat. No. 4,806,463).
Crooke and coworkers. (Crooke et al. (1992) Antimicrob. Agents Chemother. 36:527-532) described an antisense against HSV-1.
Draper et al. (1993) (U.S. Pat. No. 5,248,670) have reported antisense oligonucleotides having anti-HSV activity containing the Cat sequence and hybridizing to the HSV-1 genes UL13, UL39 and UL40.
Kean et al. (Biochemistry (1995) 34:14617-14620) have tested antisense methylphosphonate oligomers as anti-HSV agents.
Peyman et al. (Biol Chem Hoppe Seyler (1995) March; 376:195-198) have reported testing specific antisense oligonucleotides directed against the IE110 and the UL30 mRNA of HSV-1 for their antiviral properties.
Oligonucleotides or oligonucleotide analogs targeting CMV mRNAs coding for IE1, IE2 or DNA polymerase were reported by Anderson et al (1997) (U.S. Pat. No. 5,591,720)
Hanecak et al (1999) (U.S. Pat. No. 5,952,490) have described modified oligonucleotides having a conserved G quartet sequence and a sufficient number of flanking nucleotides to significantly inhibit the activity of a virus such as HSV-1.
Jairath et al (Antiviral Res. (1997) 33:201-213) have reported antisense oligonucleotides against RSV.
Torrence et al (1999) (U.S. Pat. No. 5,998,602) have reported compounds comprising an antisense component complementary to a single stranded portion of the RSV antigenomic strand (the mRNA strand), a linker and a oligonucleotide activator of RNase L.
Qi et al. (Zhonghua Shi Yan He Lin Chuang Bing Du Xue Za Zhi (2000) 14:253-256) have reported testing antisense PS-ODNs in Coxsackie virus B3.
International publication WO9203051 (Roizman and Maxwell) describes methylphosphonate antisense oligomers which are complementary to vital regions of HSV viral genome or mRNA transcripts thereof which exhibit antiviral activity.
Guanosine/thymidine or guanosine-rich phosphorothioate oligodeoxynucleotides (GT-PS-ODNs) have been reported to have antiviral activity. The article stated that “several different PS-containing GT-rich ODNs (B106-140, I100-12, and G106-57) all 26 or 27 nt in length, were just as effective at reducing HIV-2 titers as GT-rich ODNs consisting of 36 (B106-96. B106-97) or 45 nt (Table 4).” (Fennewald et al., Antiviral Res. (1995) 26:37-54).
In U.S. Pat. No. 6,184,369, anti-HIV, anti-HSV, and anti-CMV oligonucleotides containing a high percentage of guanosine bases are described. In preferred embodiments, the oligonucleotide has a three dimensional structure and this structure is stabilized by guanosine tetrads. In a further embodiment, the oligonucleotide compositions of the invention have two or more runs of two contiguous deoxyguanosines The patent claims a G-rich ODN that includes at least two G residues in at least two positions.
Cohen et al. (U.S. Pat. Nos. 5,264,423 and 5,276,019) described the inhibition of replication of HIV, and more particularly to PS-ODN analogs that can be used to prevent replication of foreign nucleic acids in the presence of normal living cells. Cohen et al describe antiviral activity of antisense PS-ODNs specific to a viral sequence. They also describe testing polyA, polyT and polyC PS-ODN sequences of 14, 18, 21 and 28-mers and indicate an antiviral effect of those PS-ODNs.
Matsukura et al. (Matsukura et al (1987) Proc Natl Acad Sci USA 84:7706-7710) later published the result described in Cohen et al, US patents above.
Gao et al (Gao et al (1989) J Biol Chem 264:11521-11526), describe the inhibition of replication of HSV-2, by PS-ODNs by testing of polyA, polyT and polyC PS-ODN sequences in sizes of 7,15, 21 and 28 nucleotides.
Archambault, Stein and Cohen (Archambault et al (1994) Arch Virol 139:97109) report that a PS-ODN polyC of 28 nucleotides is not effective against HSV-1.
Stein et al (Stein et al. (1989) AIDS Res Hum Retrovir 5:639-646), published results concerning additional data on anti-HIV ODNs, generally of 21-28 nucleotides in length.
Marshal et al. (Marshall et al. (1992) Proc. Natl. Acad. Sci. USA 89:6265-6269) describe anti-HIV-1 effect of phosphorothioate and phosphorothioate poly-C oligos of 4-28 nucleotides in length.
Stein & Cheng (Stein et al. (1993) Science 261:1004-1012), in a review article, mention the antiviral activity of non specific ODNs of 28 nucleotides, stating that “the anti-HIV properties of PS oligos are significantly influenced by non-sequence-specific effects, that is, the inhibitory effect is independent of the base sequence.”
In a review article Lebedeva & Stein (Lebedeva et al (2001) Annul Rev Pharmacol 41:403-419) report a variety of non-specific protein binding activity of PS-ODNs, including viral proteins. They state that “these molecules are highly biologically active, and it is often relatively easy to mistake artifact for antisense”.
Rein et al. (U.S. Pat. No. 6,316,190) reported a GT rich ON decoy linked to a fusion partner and binding to the HIV nucleocapsid, which can be used as an antiviral compound. Similarly, Campbell et al. (Campbell et al (1999) J. Virol. 73:2270-2279) reported PO-ODN with a TGTGT motif binding specifically to the nucleocapsid of HIV but with no references to an antiviral activity.
Feng at al. (Feng et al. (2002) J. Virol. 76:11757-11762) described A(n) and TG(n) PO-ODNs binding to the recombinant HIV nucleocapsid but with no data nor references to an anti-HIV activity.
Antisense ODNs developed as anticancer agents, antiviral agents, or to treat others diseases are typically approximately 20 nucleotides in length. In a review article (Stein, Calif., (2001) J. Clin. Invest. 108:641-644), it is affirmed that “the length of an antisense oligonucleotide must be optimized: If the antisense oligonucleotide is either too long or too short, an element of specificity is lost. At the present time, the optimal length for an antisense oligonucleotide seems to be roughly 16-20 nucleotides”. Similarly, in another review article (Crooke, S T (2000) Methods Enzymol. 313:3-45) it is stated that “Compared to RNA and RNA duplex formation, a phosphorothioate oligodeoxynucleotide has a Tm approximately −2.2° lower per unit. This means that to be effective in vitro, phosphorothioate oligodeoxynucleotides must typically be 17- to −20-mer in length . . . ”.
Caruthers and co-workers (Marshall et al. (1992) Proc. Natl. Acad. Sci. USA 89:6265-6269) reported anti-HIV activity of phosphorodithioate ODNs (PS2-ODNs) for a 12mer polycytidine-PS2-ODN and for a 14mer PS2-ODN. No other sizes were tested for anti-HIV activity. They also reported the inhibition of HIV reverse transcriptase (RT) for 12, 14, 20 and 28mer polycytidine-PS2-ODNs. Later, (Marshal et al (1993) Science 259:1564-1570) reported results showing sequence specific inhibition of the HIV RT. The same group published data for PS2-ODNs in several patents. In U.S. Pat. Nos. 5,218,103 and 5,684,148, PS2-ODN structure and synthesis is described. In U.S. Pat. Nos. 5,452,496, 5,278,302, and 5,695,979 inhibition of HIV RT is described for PS2-ODNs not longer than 15 bases. In U.S. Pat. Nos. 5,750,666 and 5,602,244, antisense activity of PS2-ODNs is described.